1. Field of the Invention
The present invention relates to a Pb-free solder alloy, particularly to a Bi—Al—Zn-based Pb-free solder alloy.
2. Description of the Related Art
In recent years, restrictions on chemical substances harmful to the environment have become increasingly stringent, and restrictions on solder materials used to join electronic parts or the like to substrates are no exception. From long ago, Pb (lead) has been continued to be used as a main component of solder materials, but has already been designated as a restricted substance by, for example, RoHS Directive. For this reason, solders containing no Pb (hereinafter, also referred to as “Pb-free solders”) have been actively developed.
Solders used to join electronic parts to substrates are broadly divided into high-temperature solders (about 260° C. to 400° C.) and low- and middle-temperature solders (about 140° C. to 230° C.) based on their service temperature limits. Among them, as for low- and middle-temperature solders, Pb-free solders mainly containing Sn have already been practically used. For example, Japanese Patent Kokai No. 11-077366 discloses a Pb-free solder alloy composition containing Sn as a main component, 1.0 to 4.0% by mass of Ag, 2.0% by mass or less of Cu, 0.5% by mass or less of Ni, and 0.2% by mass or less of P. Japanese Patent Kokai No. 8-215880 discloses a Pb-free solder alloy composition containing 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance Sn.
On the other hand, high-temperature Pb-free solder materials also have been developed by various organizations. For example, Japanese Patent Kokai No. 2002-160089 discloses a Bi/Ag brazing filler material containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500° C. Japanese Patent Kokai No. 2006-167790 discloses a solder alloy obtained by adding a binary eutectic alloy to a eutectic alloy containing Bi and by further adding an additive element thereto, and describes that this solder alloy is a quaternary or higher solder, that is, a multi-component solder, but it is possible to adjust its liquidus-line temperature and to reduce variations in composition.
Japanese Patent Kokai No. 2007-281412 discloses a solder alloy obtained by adding Cu—Al—Mn, Cu, or Ni to Bi, and describes that when such a solder alloy is used to join a power semiconductor device having a Cu surface layer to an insulator substrate having a Cu surface layer, an undesired reaction product is lese likely to be formed at a joint interface between the solder and each of the Cu layers so that the occurrence of defects such as cracks can be suppressed.
Japanese Patent No. 3671815 discloses a solder composition containing, based on the total mass of the solder composition, 94.5% by mass or more of Bi as a first metal element, 2.5% by mass of Ag as a second metal element, and a total of 0.1 to 3.0% by mass of at least one selected from the group consisting of Sn: 0.1 to 0.5% by mass, Cu: 0.1 to 0.3% by mass, In: 0.1 to 0.5% by mass, Sb: 0.1 to 3.0% by mass, and Zn: 0.1 to 3.0% by mass as a third metal element.
Japanese Patent Kokai No. 2004-025232 discloses a Pb-free solder composition containing a Bi-based alloy containing at least one of Ag, Cu, Zn, and Sb as an accessory component and 0.3 to 0.5% by mass of Ni, and describes that this Pb-free solder has a solidus-line temperature of 250° C. or higher and a liquidus-line temperature of 300° C. or less. Japanese Patent Kokai No. 2007-181880 discloses a binary alloy containing Bi, and describes that this binary alloy has the effect of suppressing the occurrence of cracking in the inside of a soldering structure.